RM0020 datasheet(51/69 Pages) STMICROELECTRONICS

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RM0020

Function API

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unsigned short N;

void main(void)

{

/* filter the samples in x with sixth-order IIR filter, */

/* write result into y */

N = 256;

iir_float_casc(N, x, y, c, s, 3);

}

6.27

iir_frac16_1st - frac16 first-order IIR filter

Function call:

void iir_frac16_1st(unsigned short N, short *x, short *y, short *c,

short *s);

Arguments:

Description:

Computes the first-order IIR filter on frac16 data. The input samples are stored in the

array x, output samples are written to the array y. There is used the arithmetic with

saturation so the output will never overflow.

Algorithm:

Equation 45

for each n from 0 to N-1

Performance: See Section 7 and Table 58.

Example 27. iir_frac16_1st

#include "libdsp2.h"

/* #pragma and ALIGN macros used to align to 4 bytes */

#ifdef __ghs__

#pragma alignvar (4)

#endif

ALIGN_DCC(4)

Table 27.

iir_frac16_1st arguments(1)

The x,y,c,s data are in fractional 16-bit format in range -1 to 1. The arrays x,y,s must be word

aligned, the array c must be half-word aligned (implicit alignment of short data). There must be 4

bytes of readable memory behind the array x. There are returned new values of x(-1), y(-1) in the

array s to be ready for next function call.

number of input and output samples (N must be multiple of 4)

array of input samples of length N, x(0) x(1) ... x(N-1)

out

array of output samples of length N, y(0) y(1) ... y(N-1)

array of filter coefficients, c[3] = {b0, b1, a1}

in/out

array of previous input and output values (state vector), s[2] = {x(-1),

y(-1)}



xn

 b1

xn 1

–

 a1

yn 1

–



–

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